Unlike conventional telephones, portable telephones do not typically reside in a fixed location on a desktop, table or wall. Portable telephones often travel with their owners in cars, offices, parks, golf courses, etc. Accordingly, both the physical environment and acoustic environment surrounding the telephone change.
This environmental variability may prevent or hinder the user from hearing the ringing of the telephone. For example, if the user moves to a noisy environment, the ambient noise may interfere with the user being able to hear the ringing tones of the telephone. Similarly, if the user carries the telephone in a pocket, briefcase or purse, for example, the ringing tones may be muffled or reflected by the environment immediately surrounding the telephone, thereby also obscuring the sound of the ringer. In either scenario, the user may not be able to hear the ringing tones, thereby possibly missing a call.
Portable telephones typically provide a means for the user to manually adjust the volume (ie: amplitude) of the ringing tones. Such manual methods require the user to pre-select the desired volume of the ringing tone in anticipation of the required volume at the time that an incoming call subsequently arrives. However, if the user forgets (or simply neglects) to increase the volume of the ringing tones prior to entering a noisy location or prior to placing the telephone in a muffling environment (a briefcase or pocket, for example), the user may not then be able to hear the ringing tones. Alternatively, if the user has previously set the ringing tones to a loud volume and the user moves to a quiet environment, the resulting volume of the ringing tones may startle or disturb those in the local vicinity.
One known method of addressing the problem of increasing an alerting signal to a volume sufficient to be heard by a user has been implemented in some models of consumer alarm clocks and clock radios. Using this method, the initial volume of the alarm is set at a pre-determined level. If the user fails to intervene (eg: if the user fails to turn off the alarm), then after a pre-determined time interval, the volume of the alarm is increased by a pre-determined amount. In this manner, the volume of the alarm will continue to increase until it reaches some pre-determined maximum volume or the need for the alarm ceases. However, such a method would be of marginal effectiveness with respect to telephony, since an unanswered call will typically either be abandoned by the calling party or else answered by an answering machine or voice mail system prior to the time required for the volume of the alarm to reach the necessary level to be heard by the user.
The prior art also reveals, for example, European patent application No. 92302479.8 in the name of Nokia Mobile Phones Ltd., published on Oct. 7, 1992, disclosing a telephone apparatus which senses the ambient noise level and adjusts the volume of the ringing tones accordingly. While such a device may operate effectively when the telephone is located in the same open space as the user, when the phone is located in a pocket, briefcase or purse, for example, the apparatus disclosed in the Nokia application would evaluate the ambient noise level without taking into account that the ringing tones generated by the telephone could be significantly muffled or obstructed by the environment immediately surrounding the telephone (pocket fabric, briefcase or purse). Indeed, if the Nokia device is located in an enclosed muffling environment (eg: a purse or briefcase), the amplitude of the ambient noise will be attenuated by the surrounding muffling materials. The Nokia device may therefore be "tricked" and fail to increase the volume of the ringing when such an adjustment is required. Further, while the device contemplated by the Nokia patent considers the amplitude of the ambient noise, it fails to consider the frequency or temporal characteristics of the ambient noise.
The prior art does reveal a method which attempts to determine whether or not a telephone is located within a briefcase. For example, (the Derwent English language summary of) Japanese application 2058952 in the name of Matsushita Elec Ind KK, published on Feb. 28, 1990, discloses a telephone device which increases the volume of the ringing tone when the device detects low lighting (apparently, low lighting suggests that the telephone is located within a briefcase). However, such a solution does not take into account the possibility that the telephone may be located in a dark room beside the user rather than in a briefcase. As well, this solution does not consider the different degrees to which the local environment may muffle the ringing tone. For example, the loudness of the ringing tone may have to be increased if the telephone is transferred from a thin fabric pocket to a more substantial briefcase.